1. Field of the Invention
This invention relates to the cleaning of heat exchangers of the kind comprising tubes through which water or another heat exchanging fluid flows.
2. Description of the Prior Art
A known installation, shown diagrammatically in FIGS. 1 to 3 of the accompanying drawings, comprises an injection tube 1 for continually injecting into the fluid which flows through the exchanger, upstream of the latter (FIG. 1), cleaning balls 2 composed of a flexible and compressible material.
These balls, which have a diameter slightly greater than that of the tubes of the heat exchanger, are carried along by the fluid into the tubes, which they flow through, thus ensuring that the tubes are cleaned.
A separator device 3 located in the outlet pipe of the heat exchanger allows the balls to be collected and conveyed by means of a pump 4 towards the injection tube 1.
The separator device (FIGS. 2 and 3) generally comprises, upstream, two converging grids 5 made up of parallel longitudinal bars, the distance between the bars being less than the diameter of the balls. These grids are each at an angle of from 20.degree. to 30.degree. with respect to the direction of fluid flow. They intercept the balls which, driven along by the force of the current, slide along the bars towards a passage 6 formed by two parallel surfaces situated downstream of the grids (FIG. 2).
The balls are then intercepted by other grids 7 positioned downstream of the grids 5 in such a way that their bars, also longitudinal and parallel, form an angle of from 20.degree. to 30.degree. with respect to the direction of fluid flow. The balls 2 slide along these bars towards inlet pipes 8 of the pump 4.
The various grids of this separator device, the purpose of which is to divert the balls from the fluid flow, also trap the various impurities and detritus of all types which are carried along by the fluid. These, therefore, build up progressively on the grids and it is necessary to ensure periodic cleaning.
This cleaning is generally carried out by the following method: the balls are first of all collected in a sieve 9 by operating a valve 10 located downstream from the pump 4, which ensures that the balls 2 are held in a filtering basket 11 contained in the sieve.
The grids 5 are pivotable about transverse axes 12 parallel to each other, a mechanism 13, such as a crank, allowing them to be turned (FIGS. 2 and 3).
When all the balls have been collected in the sieve 9, the grids 5 are pivoted one towards the other about their axes by means of the cranks, so that the grids are reversed with respect to the direction in which the fluid flows through them, the entry surface of each grid becoming the outlet surface. The impurities held by the grids are thus dislodged and entrained in the fluid.
A similar operation is carried out with the grids 7 which pivot around their axes 14, moved by handwheels 15, for example.
When the grids 5 and 7 have remained in this counter-current position for a sufficient period for cleaning, they are returned to their initial positions, and the valve 10 in the sieve is operated to allow the balls to circulate once again.
The installation which has just been briefly described has some disadvantages:
A large proportion of the impurities held by the grids 5 slide along the bars of these grids, as do the balls 2 themselves. These impurities are then held by the grids 7. A proportion of these impurities slide along the bars of the grids and are sucked in by the pump 4, but some of them remain wedged on the grids 7.
Consequently, the grids 7, the surfaces of which are much smaller than those of the grids 5, become clogged up much more quickly than the grids 5.
It is therefore the clogging up of the downstream grids 7 which determines the frequency of washing the grids, during which washing the cleaning of the exchanger tubes is no longer effected.
Furthermore, in installations where the fluid is particularly dirty, the clogging up of the grids 7 may be such that washing by the fluid flow is not enough to dislodge all the impurities which are held, so that the grids become permanently clogged up.
Finally, when the clogging up of these grids reaches too high a level, the balls 2 slide less and less easily along the bars and a certain number of them remain immobile on the grids. Not only do these immobile balls no longer take part in the cleaning of the tubes, but they are lost for good since they are carried along with the impurities during the cleaning of the grids by the fluid flow. The loss of these balls, which have to be replaced by new balls, considerably increases the cost of operating the installation.
The main object of this invention is to remedy the disadvantages set out above.